The colorful clownfish is one of the best tenants in all the oceans. In exchange for protection from predators and a few scraps of food, it protects its household from invaders, keeps things clean, provides key nutrients, and even airs things out.
Clownfish, with its sea anemone home in the background. Credit: Ritiks, WikipediaThe clownfish’s home is a sea anemone — a mass of swaying tentacles lined with deadly stingers. Just about anything that swims into the tentacles is doomed — except the clownfish. Its skin is lined with a layer of mucus that protects the fish from harm.
A young clownfish doesn’t just dart into any old anemone, though. It picks one out and stays there. It first swims gingerly around the anemone, allowing the tentacles to barely touch different parts of its body. Over a period of days or hours, it becomes acclimated to its chosen home and settles in.
The clownfish lives by eating scraps of food that the anemone misses, as well as parasites and dead cells on the host’s tentacles. In addition to keeping the place clean, the clownfish performs a long list of additional services for its host. It’s quite aggressive, and it chases away butterfly fish and others that can eat the tentacles. Its wastes are rich in nitrogen and ammonia, which act as a sort of fertilizer, helping the host grow. And it frequently darts to and fro through the tentacles, flapping its fins as it does so. That increases the flow of water over the anemone, bringing more oxygen.
So the clownfish is more than just a pretty face — it helps its sedentary host survive the rigors of the deep.
